Enhanced complexation and electrostatic attraction through fabrication of amino- or hydroxyl-functionalized Fe/Ni-biochar composite for the adsorption of Pb(II) and Cd(II)

To enhance Pb(II) and Cd(II) elimination, new composites (FeNi-RSN-(OH)(NH 2 ) and FeNi-RSN-OH) were fabricated by loading biochar with Fe-Ni nanoparticles and functionalizing biochar by amination/hydroxylation in the study. The maximum sorption capacities of both adsorbents toward Pb(II)/Cd(II) were 217.09/209.36 mg/g and 242.15/229.52 mg/g, respectively, which were 4.30–4.79 times higher than those of the raw biochar. The significantly enhanced adsorption capacity could be attributed to the increased O/N-containing groups and Fe-Ni nanoparticles on the adsorbent surface. The introduction of Fe-Ni nanoparticles and O/N-containing groups promoted the complexation and electrostatic interactions and made them playing major roles in the adsorption. Besides, ions exchange and physical adsorption played non-negligible roles in the adsorption process. Additionally, the both adsorbents exhibited favorable anti-interference ability and cycling stability. Taken together, the study revealed that the new biochar composites of FeNi-RSN-(OH)(NH 2 ) and FeNi-RSN-OH could be used as a reusable magnetic adsorbents with promising prospect in current practice for the effective remediation of heavy metals-bearing wastewater. The study not only provided a feasible design, synthesis and optimization strategy of biochar for heavy metals contaminants removal, but also realized the sustainable utilization of waste.